The invention relates to the field of methods for measuring inside a continuous blanket of mineral or plant fibres, in particular mineral wool, of the glass wool or rock wool type. These blankets are intended to be cut so subsequently to form for example thermal and/or acoustic insulation panels or rolls.
The manufacture of such blankets of insulating fibres comprises primarily fiberizing and depositing fibres on a perforated mobile transporter or conveyor. The newly formed mass of fibres is pressed onto the conveyor with the aid of suction boxes that are arranged under the conveyor on which they are deposited. During fiberizing, a binder is sprayed in the form of a solution or suspension in a volatile liquid such as water onto the drawn fibres, this binder having properties of adhesivity and usually comprising a heat-curable material, such as a thermosetting resin.
The primary layer of relatively loose fibres on the collector conveyor is then transferred to a heating device commonly known in the field in question as a crosslinking oven. The blanket of fibres passes through the oven along its entire length, by virtue of additional perforated conveyors. These are frequently two endless belts that face one another and are spaced apart by a distance appropriate for determining the thickness of the blanket which is formed. Each belt of the conveyors is furthermore formed by flights that form mutually articulated grilles that are perforated so as to be permeable to air and other gases emitted during the heating of the blanket. Such a blanket thus has a greater or lesser density depending on the degree of compression exerted by the two conveyors in the oven.
As it passes through the oven, the blanket is simultaneously dried and subjected to a specific thermal treatment which brings about the polymerization (or “curing”) of the thermosetting resin of the binder present on the surface of the fibres.
The procedure used to bring about the curing of the binder consists in passing heated air through the blanket such that the binder present throughout the thickness of the blanket is progressively brought to a temperature greater than its curing temperature. To this end, the crosslinking oven is composed of an enclosure which forms a chamber closed around the blanket and in which there is disposed a set of boxes that are supplied with hot air from burners that is set into circulation by fans. Each box thus defines an independent heating zone in which the specific heating conditions are regulated. The boxes are separated by walls that have openings for the blanket and the upper and lower conveyors. The use of a plurality of boxes thus allows a graduated increase in the temperature of the blanket throughout its passage through the oven and avoids the appearance of hot points resulting from locally excessive heating or alternatively the presence within the blanket of zones in which the binder has not been fully polymerized. An oven used in the method for manufacturing mineral wool thus very commonly comprises a multitude of boxes (for example between 3 and 10) and also known means for establishing variable thermal conditions within each box.
Currently, the use of new alternative binders, replacing the phenol-formaldehyde resins, is making it more difficult to control the conditions of the method for curing the blanket of fibres in a conventional oven as described above. Such binders, which generally do not contain formaldehyde and are sometimes known as “green binders”, in particular when they are at least partially derived from a renewable, in particular plant-based, starting material, in particular of the type derived from hydrogenated or non-hydrogenated sugars, for example as described in applications WO 2009/080938 and WO 2010/029266, very often require very good regulation of the curing temperatures in order to reach the thermoset state, the range of curing temperatures being narrower. Very particularly, the binder should be subjected to a temperature of between a minimum for achieving curing thereof and a maximum beyond which it rapidly degrades, thus ultimately resulting in impaired mechanical properties of the end product, even after it has been installed. The difference between the minimum and the maximum, depending on the type of green binder, may be around just 20° C., or even less. Temperature control throughout the thickness and width of the blanket of fibres therefore requires novel techniques and in particular changes in the very design of the ovens.